LI-COR LI-6400, Руководство пользователя

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OPENÕs System Variables
Band Broadening Correction for Water Vapor
Using the LI-6400 14-25
binary mixture that is 80% (v/v) nitrogen and 20% oxygen at a total pressure
of 100 kPa is
P
e
= 80 (1) + 20 (.81) = 96.2 kPa.
Equivalent pressure can be written in terms of mole fractions and total pres-
sure. For air with dry gas mole fractions
X
i
, and water vapor mole fraction w ,
(14-41)
is typically small ( ) for gas exchange measurement condi-
tions and is neglected. LI-COR analyzers are calibrated with CO
2
in dry air,
not nitrogen. If dry air is taken as reference instead of nitrogen, then (14-41)
becomes
(14-42)
where . The foreign gas broadening coefficient for
water vapor is denoted in (14-42) to indicate that it uses dry air as refer-
ence, instead of nitrogen.
A calibration equation similar to (14-38) that includes the pressure broaden-
ing effects of variable water vapor can be obtained by substituting
P
e
for P in
(14-33) and (14-34), and carrying through the subsequent steps to give
Table 14-9. Typical foreign gas and self-broadening coefficients for
the CO
2
4.26 µm absorption band (Burch et. al. 1962).
Gas Broadening
Coefficient
Comment
N
2
1.00 Foreign Gasses
O
2
0.81
H
2
1.17
A 0.78
He 0.59
H
2
O ?
CO
2
1.30 Self Broadening
P
e
P 1
a
w
1 Ð
( )
w
a
i
1 Ð
( )
X
i
å
+ +
[ ]
=
X
CO
2
3.5
4 Ð
´
10
P
e
P 1
a
w
1 Ð
( )
w +
[ ]
=
P c w ( ) =
c w ( ) 1
a
w
1 Ð
( )
w +
[ ]
=
a
w